Statistical analysis of our results has show no significant difference between habitat and allele frequencies of our samples tested. We can come to conclude that it is hard to determine a precise reason for the polymorphism of C. nemoralis as it takes more than one evolutionary process to contribute to the difference of allele frequencies. Selection may still be a significant factor for the polymorphism of C. nemoralis however there can also be many other possibilities that were not included in our study.
Genetic drift - could be an explanation for differences in allele frequencies. Random drift from neighbouring populations can affect allele frequencies over generations.
Bottleneck?
Gene flow – continuous gene flow between populations can limit natural selection. As the high and low altitude snails are not isolated from each other there may be constant gene flow between them and this can prevent the alleles for different polymorphic traits becoming separated and showing a distinct differences between them.
As we have not carried out any tests for gene flow, we do not know the extent of gene flow over generations between the populations.
Mutation – can contribute advantageous as well as disadvantages alleles to population gene pools.
Other types of selection pressure may be acting on the populations e.g. not altitude but for example sunlight, grazing habits, predation etc.
Chance
Linkage/Epistasis
Jones et al 1977. “Polymorphism in Cepaea: A Problem with Too Many Solutions?”
Although sampling error can be responsible for our insignificant results, it is unlikely that this is the only reason as we did conduct our sampling at 5 different sites to eliminate any chance of sampling error in our method. Other limitations may include:
The sites we sampled from may not have enough altitude difference between them.
Different phenotypes may be due to a direct effect of the environment, not a genetic difference.
We do not know for sure that it is colder in the valley bottom.
Brown shells or much banded shells may have been harder to see and too look for, therefore may have been overlooked when sampling this could have given an unfair representation of shell colour in the samples collected.
Improvements
Repetition – larger sample size needed and from more areas
Also replication of results from the same habitats are necessary, repeated samples should be taken from the same 5 sites in order to provide more reliable results.
Elin Grigorian, Sharlini Varatharajah
Discussion
Statistical analysis of our results has show no significant difference between habitat and allele frequencies of our samples tested. We can come to conclude that it is hard to determine a precise reason for the polymorphism of C. nemoralis as it takes more than one evolutionary process to contribute to the difference of allele frequencies. Selection may still be a significant factor for the polymorphism of C. nemoralis however there can also be many other possibilities that were not included in our study.
Genetic drift - could be an explanation for differences in allele frequencies. Random drift from neighbouring populations can affect allele frequencies over generations.
Bottleneck?
Gene flow – continuous gene flow between populations can limit natural selection. As the high and low altitude snails are not isolated from each other there may be constant gene flow between them and this can prevent the alleles for different polymorphic traits becoming separated and showing a distinct differences between them.
As we have not carried out any tests for gene flow, we do not know the extent of gene flow over generations between the populations.
Mutation – can contribute advantageous as well as disadvantages alleles to population gene pools.
Other types of selection pressure may be acting on the populations e.g. not altitude but for example sunlight, grazing habits, predation etc.
Chance
Linkage/Epistasis
Jones et al 1977. “Polymorphism in Cepaea: A Problem with Too Many Solutions?”
Although sampling error can be responsible for our insignificant results, it is unlikely that this is the only reason as we did conduct our sampling at 5 different sites to eliminate any chance of sampling error in our method. Other limitations may include:
The sites we sampled from may not have enough altitude difference between them.
Different phenotypes may be due to a direct effect of the environment, not a genetic difference.
We do not know for sure that it is colder in the valley bottom.
Brown shells or much banded shells may have been harder to see and too look for, therefore may have been overlooked when sampling this could have given an unfair representation of shell colour in the samples collected.
Improvements
Repetition – larger sample size needed and from more areas
Also replication of results from the same habitats are necessary, repeated samples should be taken from the same 5 sites in order to provide more reliable results.